Takeoff is measured in hours and days. An estimator opens a drawing set, sets the scale by hand, and works page by page counting fixtures, tracing linear runs and totalling areas — then repeats the whole thing when the set is revised.
Most of a drawing set is irrelevant to any one trade. An electrical estimator does not need the landscaping sheets, but still has to open them to find out. The volume of pages is itself part of the cost.
And generic automation does not fit. Exteriors, plumbing, electrical and mechanical each count different things in different ways, so a tool that measures everything the same way produces numbers nobody can bid from.
Estimators also will not accept a black box. If the software says 4,180 square feet and the estimator disagrees, they need to change it — and everything downstream has to follow that correction.